In today's terms it is: July XXXI MCMXCIX or as VII-XXXI-MCMXCIX
But the Romans themselves would have probably calculated the number 1999 on an abacus counting device as MDCCCCLXXXXVIIII and simplified it to IMM (-1+2000 = 1999)
Today's rules governing the Roman numeral system were introduced during the Middle Ages but that was centuries after the disappearance of the Roman Empire.
The equivalent of 31 as a Roman numeral is XXXI
XXXI is the Roman numeral for the number 31.
As a Roman numeral 31 is XXXI
XXXI
31
It is 31 in Hindu-Arabic numerals
31 in Roman numerals is XXXI which is equivalent to: 10+10+10+1 = 31
XXXI.VIII.MMXII
31.
XXXl ? 31
If you mean XXXI then it is equivalent to 31
It is: XXXI-III-MMXII